1. Field of the Invention
The present invention relates to a zoom lens barrel provided with a zoom type photographic lens (hereinafter referred to as a zoom lens) which facilitates telephotographing and wide angle photographing by making adjustable a distance between a plurality of lens groups.
2. Related Background Art
The recent compact camera which has multi-functions uses a zoom lens which can freely photograph within a range from a telephotographic position to a wide angle position. Further, a camera of a barrel sinking type in which the zoom lens is moved in the camera body is generally used in order to satisfy the requirements in that the camera be made small and thin.
The zoom lens of this type has a structure that at least two set of lens groups are reciprocatingly arranged in the lens barrel so that the composite focal length is varied by changing the distance between the lens groups to photograph at any image magnification.
The conventional zoom lens barrel having a zoom lens of this type as disclosed in Japanese Patent Application Laid-Open No. 4-278932 comprises a linear movement guide tube provided at the side of the camera body and provided with a plurality of axially extending guide grooves formed in the outer peripheral surface of the guide tube, a plurality of lens groups held by the respective lens holders having engaging pins inserted in the guide grooves and which reciprocate along the optical axis, and a zoom cam ring rotatably mounted on the outer peripheral surface of the linear movement guide tube and provided in the outer peripheral surface with a plurality of cam grooves which incline with respect to the optical axis and in which the engaging pins of the corresponding lens holders are respectively inserted through the guide grooves.
In order to achieve quick photographing and improve operability of the compact camera provided with such a zoom lens barrel, the zoom lens makes zooming operation in such a manner that the zoom cam ring is rotated by a driving motor assembled in the camera body to reciprocate the lens groups together with the lens holders, whereby the distance between the lens groups is changed and the composite focal length is varied.
FIG. 15 is a developed view of the zoom lens cam ring, showing the shapes of guide grooves and cam grooves of the zoom lens barrel and the relationship therebetween. A zoom cam ring 1 having a circumferential length A is used for reciprocating two lens groups, and has a plurality of sets of cam grooves (such as three first cam grooves 2 and three second cam grooves 3) formed on the peripheral surface and alternately arranged in a circumferential direction.
The first cam groove 2 is for reciprocating a respective first lens group disposed closer to an object along a respective one of first guide grooves 4 of a linear movement guide tube and forms an inclined zooming groove intersecting with the optical axis at a predetermined angle. Each engaging pin 5 provided on a lens holder for holding the first lens group engages both the respective cam groove 2 and the respective guide groove 4. Each second cam groove 3 is for reciprocating the second lens group disposed remote from the object along the respective one of second guide grooves 6 of the linear movement guide tube.
Each second cam groove 3 is bent into a shallow V shape so that it comprises a barrel sinking groove portion 3a disposed in parallel with a film surface extending circumferentially of the zoom cam ring 1 and a zooming groove 3b intersecting with the optical axis at a predetermined angle.
Each engaging pin 7 provided on the lens holder for holding the second lens group engages the respective second cam groove 3 through the respective guide groove 6. The barrel sinking groove portion 3a of each second cam groove 3 is formed at the side of the wide end of the zoom cam ring 1.
The end a of the barrel sinking groove portion 3a which is remote from the zooming groove 3b is disposed at the end of the first cam groove 2 which is at the side of the sinking barrel, i.e., at the vicinity of the end a of the first cam groove 2 which is remote from the object. This makes the distance between the two lens groups as small as possible when the zoom lens barrel is sunk in the camera body at the non-photographing time, whereby the camera is made thin and small.
The angle of inclination .alpha. (the angle between the zooming groove 3b and the film surface) of each zooming groove 3b is set to be larger than the angle of inclination .beta. of the first cam groove 2. The first guide grooves 4 and the second guide grooves 6 are formed close to each other in the periphery of the linear movement guide tube and in parallel with the optical axis so that they restrict rotation of the lens groups and define moving strokes of the lens groups.
At the non-photographing time when the lens groups are sunk in the camera body, the engaging pins 5 and 7 are disposed at the ends of the first and second cam grooves 2 and 3 which are remote from the object, i.e., at the barrel sinking end positions a, as shown in FIG. 15. When the zoom cam ring 1 is rotated from this state in the direction shown by an arrow 8, the engaging pins 5 and 7 are moved to wide angle side ends (wide angle positions) b to increase the distance between the two lens groups. As the engaging pins 5 and 7 are moved from the wide angle ends b to the telephotographic ends (telephotographic positions) c, the distance between the lens groups becomes small again.
The arrow 9 shows the direction toward the object, i.e., the zoom lens extending direction.
Hitherto, the cam ring is engaged with, for example, an outer barrel provided outside by a helicoid connection or the like. In this case, in order to remove a play between the rotating barrel and the outer barrel which is generated by the helicoid connection or the like, an urging member such as a compression coil spring or the like is provided between the rotating barrel and the outer barrel so as to urge the rotating barrel to a predetermined direction so that the rotating barrel and the outer barrel is in contact with pressure in part.
The urging member such as the compression coil spring is generally made of stainless steel or the like having a high elasticity. Since such ductile material is difficult to be machined, a sheared section of such material has a large plastic deformation so that points, flash or the like is easily generated on the sheared section.
On the other hand, since the vicinity of the sheared section of the compression coil spring serves as a contacting surface to the rotating barrel or the outer barrel, if the sheared section has points or the like, those pointed portions can stick into the rotating barrel or the outer barrel in some cases. As a result, the rotating barrel can not rotate smoothly.
In a compact camera provided with a zoom lens barrel as described above, it is desirable that the distance between two lens groups be made as small as possible, and more specifically it is preferred that the distance be substantially zero in the barrel sinking state at the non-photographing time in order to make thin and miniaturize the camera. For structural reasons, however, it is difficult to make the difference between the lens groups zero in most cases. One reason is because the length of the sinking barrel 3a formed with each second cam groove 3 has a substantive length. Even if the strokes and the rotational angles of the first and second cam grooves are equal to each other, the length of the barrel sinking groove portion 3a of each second cam groove 3, as shown in FIG. 16 is larger than the one as shown in FIG. 15, when the lens system has a large sinking length from the wide angle end position b or when the stroke from the wide angle end position b to the sinking position increases to make the camera body thin and the camera compact. This causes the barrel sinking side end a of each first cam groove 2 to interfere with the wide angle side end b of the corresponding barrel sinking groove portion 3a and thus makes it difficult to extend and retract the lens groups.
If the diameter of the lens barrel is reduced to make the camera compact, the circumferential length B of the zoom cam ring 1' becomes naturally shorter, as shown in FIG. 17, than the circumferential length A of the zoom cam ring 1 as shown in FIG. 15. When the shapes and the sizes of the first and second cam grooves 2 and 3 shown in FIG. 17 are the same as those shown in FIG. 15, the rotational angle of the zoom cam ring 1' becomes large. Further, the pitches of the first and second cam grooves 2 and 3 become small, and thus their barrel sinking side ends a interfere with each other.
When the angle of inclination .beta. between the first cam grooves 2 and the film surface is set large in order to solve these problems, the rotational angle of the zoom cam ring 1' for the whole stroke can be made small and the first and second cam grooves 2 and 3 can be prevented from interfering with each other. In this case, however, a large angle of inclination .beta. increases the rotational load for rotating the zoom cam ring 1'. Thus, a large driving motor providing a large driving power is required, hindering compactness of the camera. This contradicts the reduction of the lens diameter to make the camera compact.